1. Field of the Invention
The invention relates generally to user interface controllers and pointing devices, and particularly to a method and an apparatus to sense changes in a vector field (magnetic, acceleration, or other) to determine or estimate rotations about multiple axes.
2. Description of Related Art
User interfaces to technology are an integral part of almost all technological systems. Computer functionality has been revolutionized by advances in display technology and input devices such as the keyboard and computer mouse. The line between conventional computing devices and entertainment devices is being blurred as more features are being added that require computer processors, such as digital video recorders and digital television channel guides. New input devices that are suitable for use without a desktop surface will drastically improve the user experience. Gesture based game controllers will enable the gaming market to grow more quickly.
Low power magnetic sensor technology has been primarily developed for use in navigation instrumentation, where precise compass heading has been the goal. PNI is the owner of multiple patents protecting a low power, high accuracy, Magneto-Inductive technology that enables a magnetic sensor system that can be used to accurately measure the magnetic field, in three dimensions, present at the device. One of PNI Corporation's tilt-compensated compassing module products, the TCM2, includes a mode to output mouse control signals which is documented in the TCM2 manual.
U.S. Pat. No. 5,734,371 discloses a pointing device interactive with a video and/or computer system; the pointing device comprises an inclinometer for detecting the relative vertical position relative to an initial reference position and gimbaled αzimuthal magnetic sensor generating a horizontal position indication signal.
Additional U.S. patents and applications relating to the instant invention are: U.S. Pat. No. 7,158,118, U.S. Pat. No. 7,236,156, U.S. Pat. No. 7,239,301, U.S. Pat. No. 7,262,760, U.S.20050174324, U.S.20060028446, U.S.20060130013, U.S.20060178212, U.S.20060250358, U.S.20070035518, U.S.20070113207, U.S.20070124097, U.S.20070124097, U.S.20070176896, U.S.20070247425, U.S.20070252813, U.S.20070257885, U.S.20080158154; all from Hillcrest Laboratories, Inc. Disclosures from the aforementioned patents and applications are included herein in their entirety by reference.
Hillcrest Laboratories has disclosed a series of methods which rely on a two dimensional rotation matrix to convert a first and second rotational output from a body frame into an inertial frame by calculating:R=[cos θ sin θ−sin θ cos θ]·[αyαz]wherein θ is the tilt, αy is the first rotational output and αz is the second rotational output.
A method disclosed in the instant invention generates an output from sequenced measurements of instrument or device orientation, not from rotational outputs αy and αz. As such, a two dimensional transformation, or an explicit determination of the instrument tilt is not performed. The Hillcrest method teaches a conversion from a body frame into an inertial frame; the method of the instant invention is directly measuring the inertial frame since the magnetic field is fixed in the inertial frame.